Foldable display device

ABSTRACT

A foldable display device includes a flexible display panel, a case supporting the flexible display panel, a bonding member fixing the flexible display panel to the case. The case includes a hinge portion, and supports respectively coupled to the hinge portion at opposing sides of the hinge portion. The flexible display panel includes a bendable area corresponding to the hinge portion, and planar areas respectively at opposing sides of the bendable area and corresponding to the supports of the case. The bonding member is between a support of the case and the corresponding planar area of the flexible display panel, and is displaceable with respect to the support along one of a thickness direction and a width direction of the flexible display panel when the flexible display panel is folded.

This application is a continuation application of U.S. patentapplication Ser. No. 16/561,632 filed on Sep. 5, 2019, which is acontinuation application of U.S. patent application Ser. No. 15/923,080filed on Mar. 16, 2018 and issued as U.S. Pat. No. 10,444,797 on Oct.15, 2019, which is a continuation of U.S. patent application Ser. No.15/161,338 filed on May 23, 2016 and issued as U.S. Pat. No. 9,939,847on Apr. 10, 2018, which is a continuation application of U.S. patentapplication Ser. No. 14/049,334 filed on Oct. 9, 2013 and issued as U.S.Pat. No. 9,348,369 on May 24, 2016, which claims priority to KoreanPatent Application No. 10-2013-0063507 filed on Jun. 3, 2013, and allthe benefits accruing therefrom under 35 U.S.C. § 119, the entirecontents of which are incorporated herein by reference.

BACKGROUND 1. Field

The invention relates generally to a foldable display device. Moreparticularly, the invention relates generally to a method for bonding aflexible display panel and a case of a foldable display device.

2. Description of the Related Art

A foldable display device uses a bendable flexible display panel. Thefoldable display device can be portable when folded and can realize alarge-scale screen when unfolded. As a result, the foldable displaydevice can be applied not only to mobile equipment such as a mobilephone, an ultra-mobile personal computer (“PC”), an electronic book andthe like, but also to electronic devices including, but not limited to,a television, a monitor and the like.

The foldable display device is provided with a case that supports theflexible display panel by fixing the same. The case includes a pair ofsupports coupled by a hinge portion, and the flexible display panel maybe attached to the supports by an adhesive member, excluding a centerportion thereof corresponding to the hinge portion.

SUMMARY

One or more exemplary embodiment provides a foldable display device thatcan suppress damage to a flexible display panel thereof by reducing abending stress generated in the flexible display panel when the foldabledisplay device is folded, and improve durability thereof.

A foldable display device according to an exemplary embodiment includes:a case including: a hinge portion, and supports respectively coupled tothe hinge portion at opposing sides of the hinge portion; a flexibledisplay panel including: a bendable area corresponding to the hingeportion of the case, and planar areas respectively at opposing sides ofthe bendable area and corresponding to the supports of the case; and abonding member between a support of the case and the correspondingplanar area, and displaceable with respect to the support along onedirection among a thickness direction and a plane direction of theflexible display panel when the flexible display panel is folded.

The bonding member may include a first bonding member portion, and asecond bonding member portion which is displaceable with respect to thesupport along the thickness direction of the flexible display panel whenthe flexible display panel is folded. The second bonding member portionmay be closer to the hinge portion of the case than the first bondingmember portion and may have a bonding force with respect to the supportless than that of the first bonding member portion.

The bonding force of the second bonding member portion with respect tothe support may be exceeded by an external force applied when theflexible display panel is folded, such that the second bonding memberportion is separated from the support along the thickness direction ofthe flexible display panel when the flexible display panel is folded,and the bonding force of the second bonding member portion with respectto the support may be restored when the flexible display panel isunfolded. The second bonding member portion may include a pressuresensitive adhesive and the bonding force of the second bonding memberportion with respect to the support may be in a range from about 10gf/cm to about 1,500 gf/cm.

The first bonding member portion may include an adhesive having anelongation characteristic, and may be displaceable with respect to thesupport along the plane direction of the flexible display panel when theflexible display panel is folded. The first bonding member portion mayinclude an adhesive and an elongation ratio of the first bonding memberportion may be in a range from about 100% to about 1,000%. A first edgeof the first bonding member portion may correspond to an external edgeof the corresponding planar area, and an area of the second bondingmember portion may be larger than an area of the first bonding memberportion.

The bonding member may include an adhesive having an elongationcharacteristic, and may be displaceable with respect to the supportalong the plane direction of the flexible display panel when theflexible display panel is folded. An elongation ratio of the bondingmember may be in a range from about 100% to about 1,000%.

A foldable display device according to another exemplary embodimentincludes: a case including: a hinge portion, and supports respectivelycoupled to the hinge portion at opposing sides of the hinge portion; aflexible display panel including: a bendable area corresponding to thehinge portion of the case, and planar areas respectively at opposingsides of the bendable area and corresponding to the supports of thecase; and a bonding member between a support of the case and thecorresponding planar area, and of which, a bonding area with respect tothe support is variable according to a folded state or an unfolded stateof the flexible display panel.

The bonding member may include two different types of adhesives. Thebonding member may include a first bonding member portion, and a secondbonding member portion closer to the hinge portion of the case than thefirst bonding member portion and detachable from the support accordingto the folded state or the unfolded state of the flexible display panel.

The second bonding member portion may include a pressure sensitiveadhesive, and a bonding force of the second bonding member portion withrespect to the support may be in a range from about 10 gf/cm to about1,500 gf/cm. An area of the second bonding member portion may be morethan two times an area of the first bonding member portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of this disclosure will become moreapparent by describing in further detail exemplary embodiments thereofwith reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of an exemplary embodiment of a foldabledisplay device according to the invention.

FIG. 2 is a cross-sectional view of the foldable display device of FIG.1 .

FIG. 3 and FIG. 4 are cross-sectional views of the foldable displaydevice of FIG. 2 in bent states, respectively.

FIG. 5 is a cross-sectional view of another exemplary embodiment of afoldable display device according to the invention.

FIG. 6 is a partially enlarged view of the foldable display device ofFIG. 5 .

FIG. 7 and FIG. 8 are cross-sectional views of still another exemplaryembodiment of a foldable display device in an un-folded and a bentstate, respectively, according to the invention.

FIG. 9 is a graph illustrating a luminance characteristic (percent: %)according to the number of times of bending an exemplary embodiment of afoldable display device according to the invention and a foldabledisplay device of a comparative embodiment.

FIG. 10 is a plan view of an exemplary embodiment of a pixel structureof the flexible display panel of FIG. 1 .

FIG. 11 is a cross-sectional view of the flexible display panel of FIG.10 , taken along line IX-IX.

DETAILED DESCRIPTION

The invention will be described more fully hereinafter with reference tothe accompanying drawings, in which exemplary embodiments of theinvention are shown. As those skilled in the art would realize, thedescribed embodiments may be modified in various different ways, allwithout departing from the spirit or scope of the invention. In thedrawings, the size and relative sizes of layers and regions may beexaggerated for clarity.

Unless explicitly described to the contrary, the word “comprise” andvariations such as “comprises” or “comprising” will be understood toimply the inclusion of stated elements but not the exclusion of anyother elements. The terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to belimiting of the invention. As used herein, the singular forms “a,” “an”and “the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise.

Further, it will be understood that when an element such as a layer,film, region, or substrate is referred to as being “on” another element,it can be directly on the other element or intervening elements may alsobe present. Like numbers refer to like elements throughout. As usedherein, the term “and/or” includes any and all combinations of one ormore of the associated listed items.

It will be understood that, although the terms first, second, third,etc., may be used herein to describe various elements, components,regions, layers and/or sections, these elements, components, regions,layers and/or sections should not be limited by these terms. These termsare only used to distinguish one element, component, region, layer orsection from another element, component, region, layer or section. Thus,a first element, component, region, layer or section discussed belowcould be termed a second element, component, region, layer or sectionwithout departing from the teachings of the invention.

Further, in the specification, the word “on” means positioning on orbelow the object portion, but does not essentially mean positioning onthe upper side of the object portion based on a gravity direction.

Embodiments of the invention are described herein with reference tocross-section illustrations that are schematic illustrations ofidealized embodiments (and intermediate structures) of the invention. Assuch, variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and/or tolerances, are to beexpected. Thus, embodiments of the invention should not be construed aslimited to the particular shapes of regions illustrated herein but areto include deviations in shapes that result, for example, frommanufacturing.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system). For example, “about” can mean within one or morestandard deviations, or within ±30%, 20%, 10%, 5% of the stated value.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

A foldable display device is provided with a case that supports aflexible display panel by fixing the same. The case includes a pair ofsupports coupled by a hinge portion, and the flexible display panel maybe attached to the supports by an adhesive member, excluding to a centerportion thereof corresponding to the hinge portion.

When the foldable display device is folded, an inner side of a bentportion of the flexible display panel contracts by receiving a pressurefrom the folding, and an external side of the bent portion is extendedby receiving a tension force from the folding. Since the flexibledisplay panel is restricted by the support, a stress caused bycontraction and extension cannot be released and thus remains as abending stress. Thus, the flexible display panel may be easily damageddue to the bending stress, and accordingly, durability thereof may bedeteriorated.

Hereinafter, the invention will be described in detail with reference tothe accompanying drawings.

FIG. 1 is a perspective view of an exemplary embodiment of a foldabledisplay device according to the invention and FIG. 2 is across-sectional view of the foldable display device of FIG. 1 .

Referring to FIG. 1 and FIG. 2 , a foldable display device 100 includesa flexible display panel 10, a case 20 receiving the flexible displaypanel 10 therein, and a bonding member 30 a fixing the flexible displaypanel 10 to the case 20. The bonding member 30 a may have predeterminedviscosity, and where the bonding member 30 a has such a predeterminedviscosity, the bonding member 30 a may include a viscid member.

The flexible display panel 10 includes a flexible substrate (40, seeFIG. 11 ) such as a plastic film, and displays an image by an organiclight emitting diode and a pixel circuit on the flexible substrate. Theorganic light emitting diode OLED (see FIG. 10 and FIG. 11 ) and thepixel circuit may be covered by a thin film encapsulation layer. Thethin film encapsulation layer suppresses characteristic deterioration bysealing the organic light emitting diode OLED from an externalenvironment that contains moisture and oxygen.

A transparent cover window (150, see FIG. 11 ) may be provided in anexternal side of a display side of the flexible display panel 10. Thecover window protects the flexible display panel 10 from an externalimpact or damage such as a scratch while an image of the flexibledisplay panel 10 is visible therethrough at a display side thereof. Inaddition, a touch screen panel (152, see FIG. 11 ) that senses touchoperation of a user may be provided between the flexible display panel10 and the cover window 150.

The flexible display panel 10, the touch screen panel and the coverwindow collectively form a display module. In the drawings, the flexibledisplay panel 10 in the first exemplary embodiment may be used toindicate the collective display module detailed above. A detailedstructure of the flexible display panel 10 will be described later.

The case 20 is provided at the opposite side of the display side of theflexible display panel 10, and maintains the flexible display panel 10in the constant shape by supporting the same. That is, when the foldabledisplay device 100 is unfolded, the case 20 maintains the flexibledisplay panel 10 in a substantially flat state, and when the foldabledisplay device 100 is folded or bent, the case 20 maintains the flexibledisplay panel 10 maintained in a folded or bent state.

The case 20 includes a hinge portion 21, and a pair of supports 22respectively provided at opposing sides of the hinge portion 21 andcoupled to the hinge portion 21. One side of the supports 22 facingtoward the flexible display panel 10 provides a flat surface, and thepair of supports 22 rotates with respect to the hinge portion 21 suchthat the foldable display device 100 is foldable and unfoldable aboutpivot axes at the hinge portion 22.

The hinge portion 21 may include a uniaxial hinge structure or a biaxialhinge structure. The uniaxial hinge structure includes a single rotationshaft, and the pair of supports 22 are each rotated by being coupled tothe single rotation shaft. The biaxial hinge structure includes tworotation shafts, and the pair of supports 22 are respectively rotated bybeing coupled to respective rotation shafts. A rotation shaft may definea rotation axis about which the supports 22 pivot. FIG. 1 and FIG. 2exemplarily illustrate the biaxial hinge structure, but the invention isnot limited thereto.

The flexible display panel 10 includes a bendable area 11 correspondingto and overlapping the hinge portion 21 of the case 20, and a pair ofplane (otherwise referred to as planar) areas 12 located at opposingsides of the bent area 11 and respectively corresponding to andoverlapping the supports 22 of the case 20. The bendable area 11 has asubstantially planar surface when the flexible display panel 10 isunfolded and the pair of supports 22 in parallel (e.g., on substantiallya same plane), and has an arc shape when the pair of supports 22 arepivoted to bend the flexible display panel 10 into a folded state. Thebendable area 11 is not attached to the hinge portion 21, and the planearea 12 is partially or wholly attached to the supports 22 by thebonding member 30 a. The bendable area 11 may be spaced apart from thecase 20, but the invention is not limited thereto.

The bonding member 30 a may include an acryl-based resin or asilicon-based resin, and may be located corresponding to an entiresurface of the plane area 12 or located corresponding to a part of theplane area 12. When the bonding member 30 a is located corresponding tothe part of the plane area 12, one edge of the bonding member 30 amatches (e.g., is aligned) with an external edge of the plane area 12and the opposite edge of the bonding member 30 a is located at apredetermined distance from the hinge portion 21 or the bendable area11. FIG. 1 exemplarily illustrates that the bonding member 30 a isprovided corresponding to a part of the plane area 12, but the inventionis not limited thereto.

A direct binding force to the support 22 is not generated in thebendable area 11 which is not attached to the support 22 or a part ofthe plane area 12 adjacent to and/or including the bendable area 11 ofthe flexible display panel 10.

In addition, a part of the bonding member 30 a (e.g., a second bondingmember portion 32 in the following description) has a displacement withrespect to the support 22 along a cross-sectional thickness direction(e.g., a vertical direction with reference to FIG. 2 ) of the flexibledisplay panel 10. Here the part of the bonding member 30 a having thedisplacement with respect to the support 22 means that the bondingmember 30 a is moveable along the cross-sectional thickness directionsuch that the bonding member 30 a partially moves along thecross-sectional thickness direction of the flexible display panel 10.

In the foldable display device 100 illustrated in FIG. 1 and FIG. 2 ,the collective bonding member 30 a includes more than one portion, suchas, a first and second bonding member portions 31 and 32, respectivelyhaving different displacement properties and bonding forces with respectto the supports 22. In further detail, the collective bonding member 30a includes the first bonding member portion 31 distanced further fromthe hinge portion 21 than the second bonding member portion 32, and thesecond bonding member portion 32 located in an inner side of the firstbonding member portion 31 facing the hinge portion 21. A bonding forceof the second bonding member portion 32 is lower than a bonding force ofthe first bonding member portion 31, with respect to the supports 22and/or the hinge portion 21. In an unfolded state, the first and secondbonding members 31 and 32 are in a same plane and/or a same layer of thefoldable display apparatus 100.

FIG. 3 and FIG. 4 are cross-sectional views illustrating the foldabledisplay device of FIG. 2 in bent states, respectively.

Referring to FIG. 2 to FIG. 4 , when the display device 100 is folded,the inner side of the bendable area 11 contracts due to pressure and theexternal side of the bendable area 11 is extended due to tension. Due tosuch a contraction and extension, a stress, that is, a bending stress isgenerated in the flexible display panel 10. The stress of the flexibledisplay panel 10 is maximized in the bendable area 11 and is decreasedin a distance further from the bendable area 11.

A bonding force of the second bonding member portion 32 with respect tothe supports 22 and/or the hinge portion 21 is set low enough to beovercome by external force such as a bending stress generated in theflexible display panel 10. That is, when the flexible display panel 10is folded by rotating the pair of supports 22 at the hinge portion 21, atension force is generated in the external side of the bendable area 11and the plane area 12, and the bonding force of the second bondingmember portion 32 with respect to the hinge portion 21 is exceeded dueto the tension force and the second bonding portion 32 is separated fromthe support 22. The first bonding member portion 31 may remain incontact with the support 22 when the flexible display panel 10 is bent,but the invention is not limited thereto.

Thus, as shown in FIG. 3 and FIG. 4 , when the flexible display panel 10is bent, the center portion of the flexible display panel 10 receiving arelatively large tension force is separated from the case 20 so that thebending stress is to released. That is, since the center portion of theflexible display panel 10, receiving large tension force is notrestricted by the case 20, the bending stress can be released.

When the flexible display panel 10 is unfolded, the second bondingmember portion 32 returns to an original position and contacts thesupport 22, such that a bonding force between the second bonding memberportion 32 and the case is restored by a pressure applied thereto whenthe flexible display panel 10 is unfolded. In one exemplary embodiment,for the bonding force between the second bonding member portion 32 andthe case 20 to be restored, the second bonding member portion 32 mayinclude a pressure sensitive adhesive (“PSA”) which is attachable orseparable (e.g., detached) from an element by a relatively low pressureor force.

The bonding force of the second bonding member portion 32 may be in arange from about 10 gram-force per centimeter (gf/cm) to 1,500 gf/cm.When the bonding force of the second bonding member portion 32 is lessthan about 10 gf/cm, the second bonding member portion 32 may be tooeasily separated from the support 22 under a relatively small externalforce so that flexible display panel 10 cannot be stably bonded to thecase 20. When the bonding force of the second bonding member portion 32is higher than about 1,500 gf/cm, the second bonding member portion 32is not easily separated from the support 22 when the foldable displaydevice 10 is being folded so that the bending stress is maintained(e.g., not relieved) in the flexible display panel 10.

In contrast, the first bonding member portion 31 not separated by anexternal force applied thereto, even by a strong bonding force, when thefoldable display device 100 is folded or unfolded, and thus the edge ofthe flexible display panel 10 is fixed to the support 22 by the firstbonding member portion 31.

As described, an exemplary embodiment of the foldable display device 100according to the invention has a structure in which a bonding area ofthe flexible display panel 10 with respect to the case 20 is variabledue to the bonding member 30 a. That is, only the edge of the flexibledisplay panel 10 is fixed to the case 20, and other portions of theflexible display panel 10 are selectively attached to or detached fromthe case 20. Therefore, the exemplary embodiment of the foldable displaydevice 100 illustrated in FIG. 1 to FIG. 4 can reduce or effectivelyprevent damage to the flexible display panel 10 by releasing a stressgenerated in the foldable display device 100, and improves durability.

A planar area of the second bonding member portion 32 is larger than aplanar area of the first bonding member portion 31. In one exemplaryembodiment, for example, the planar area of the second bonding memberportion 32 may be more than two times the planar area of the firstbonding member portion 31. Where the planar area of the second bondingmember portion 32 is larger than the planar area of the first bondingmember portion 31, the detachable area of the flexible display panel 10is increased to effectively reduce the bending stress of the flexibledisplay panel 10.

FIG. 5 is a cross-sectional view of another exemplary embodiment of afoldable display device according to the invention, and FIG. 6 is apartially enlarged view of the foldable display device of FIG. 5 .

Referring to FIG. 5 and FIG. 6 , a foldable display device 200 issubstantially the same as the foldable display device of FIG. 1 to FIG.4 , except that a first bonding member portion 311 of a bonding member30 b has a displacement with respect to a pair of supports 22 along aplane direction of a flexible display panel 10. The same referencenumerals are used for the same components as those of the exemplaryembodiment of FIG. 1 to FIG. 4 , and constituent elements that aredifferent from the exemplary embodiment of FIG. 1 to FIG. 4 will bedescribed.

In the foldable display device 200, the first bonding member portion 311has a displacement with respect to the support 22 along a planedirection (e.g., a vertical direction in FIG. 6 and indicated by thedownward pointing arrow) of the flexible display panel 10, and a secondbonding member portion 32 has a displacement with respect to the support22 along a thickness direction (e.g., a horizontal direction in FIG. 6 )of the flexible display panel 10. The configuration and operation of thesecond bonding member portion 32 are the same as those previouslydescribed, and therefore no further description will be provided.

The first bonding member portion 311 has an elongation characteristicsuch that the first bonding member portion 311 is extendable by anexternal force. In one exemplary embodiment, the first bonding memberportion 311 includes a highly stretchable or elastic adhesive having ahigh elongation ratio. In the foldable display device 200, an externalforce is applied to the first bonding member portion 311 along a planedirection of the flexible display panel 10 when the foldable displaydevice 200 is bent. In folding the foldable display device 200, thefirst bonding member portion 311 is elongated along the plane directionof the flexible display panel 10 and thus has a displacement withrespect to the support 22.

The first bonding member portion 311 stably fixes the edge of theflexible display panel 10 to the case 20, and at the same time, isdeformable to be elongated by a tension force generated when theflexible display panel 10 is folded, and thus the edge of the flexibledisplay panel 10 slides or is translated with respect to the case.

In further detail, when the foldable display device 200 is folded, atension force is generated in external sides of a bendable area 11 and aplane area 12, and a bonding force of the second bonding member portion32 with respect to the support is exceeded due to the tension force andthe second bonding member portion 32 is separated from the support 22.By such an action of the second bonding member portion 32, a bendingstress of the flexible display panel 10 can be primarily reduced.

Then, the first bonding member portion 311 is elongated along the planedirection of the flexible display panel 10 by the tension force appliedto the edge of the flexible display panel 10 and thus the edge of theflexible display panel 10 slides toward a hinge portion 21. By such anaction of the first bonding member portion 311, the bending stress ofthe flexible display panel 10 can be secondarily reduced.

The second bonding member portion 32 is detachable from the case 20. Incontrast, the first bonding member portion 311 remains attached (e.g.,is not detachable) from the case 20 and moves the location of the edgeof the flexible display panel 10 by being elongated by an externalforce.

The first bonding member portion 311 may include a material such as anadhesive having an elongation ratio of about 100% to about 1,000%. Sincetwo (e.g., opposing) surfaces of the first bonding member portion 311are respectively attached to the support 22 and the plane area 12, asliding effect can be acquired by using an adhesive having a relativelyhigh elongation ratio. When the elongation ratio of the adhesive is lessthan about 100%, the sliding of the flexible display panel 100 cannot besmoothly provided, and when the elongation ratio of the adhesive exceedsabout 1,000%, wrinkles may be generated in the edge of the flexibledisplay panel 10 when the foldable display device 200 is folded andunfolded.

FIG. 7 and FIG. 8 are cross-sectional views of still another exemplaryembodiment of a foldable display device in an un-folded and a bentstate, respectively, according to the invention.

Referring to FIG. 7 and FIG. 8 , a foldable display device 300 issubstantially the same as the foldable display device of FIG. 5 and FIG.6 , except that a bonding member 30 c wholly has a displacement withrespect to a support 22 along a plane direction of a flexible displaypanel 10. The same reference numerals are used for the same componentsas those of the exemplary embodiment of FIG. 5 and FIG. 6 , andconstituent elements that are different from the exemplary embodiment ofFIG. 5 and FIG. 6 will be described.

In the foldable display device 300, the bonding member 30 c is a single,unitary, indivisible member, and has a displacement with respect to thesupport 22 along the plane direction of the flexible display panel 10(e.g., a horizontal direction in FIG. 7 )

That is, the foldable display device 300 of FIG. 7 and FIG. 8 has astructure in which the second bonding member portion of the exemplaryembodiment of FIG. 5 and FIG. 6 is omitted and the first bonding memberportion is extended to a location of the second bonding member portion.

The bonding member 30 c stably fixes the flexible display panel 10 tothe case 20, and at the same time is elongated by a tension forcegenerated when the flexible display panel 10 is folded. Due to thetension force, a part of the flexible display panel 10 contacting thebonding member 30 c is slidable with respect to the case 20.

In further detail, when the flexible display panel 10 is folded, atension force is generated in external sides of the bendable area 11 andthe plane are 12, and the bonding member 30 c is elongated along theplane direction of the flexible display panel 10 by the tension force sothat the flexible display panel 10 is partially slid toward the hingeportion 21. The foldable display device 300 can reduce a bending stressgenerated in the flexible display panel 10 by such an action of thebonding member 30 c.

The bonding member 30 c may include a material such as an adhesivehaving an elongation ratio of about 100% to about 1,000%. Since two(e.g., opposing) surfaces of the bonding member 30 c are respectivelyattached to the support 22 and the plane area 12, the above-statedsliding effect can be acquired by using an adhesive having a highelongation ratio. The foldable display device 300 of FIG. 7 and FIG. 8uses one type of adhesive and therefore a manufacturing process can besimplified. However, in an alternative exemplary embodiment, the bondingmember 30 c may include more than one type of adhesive

FIG. 9 is a graph illustrating a luminance characteristic (percent:%)according to the number of times of bending an exemplary embodiment of afoldable display device according to the invention and a foldabledisplay device of a comparative embodiment.

The Exemplary embodiment in FIG. 9 represents the foldable displaydevice illustrated in FIG. 1 to FIG. 4 . The foldable display device ofthe Comparative embodiment is different from that of FIG. 1 to FIG. 4 ,in that the Comparative embodiment has a structure in which the secondbonding member portion in the foldable display device of FIG. 1 to FIG.4 is omitted and a first bonding member portion is extended to alocation of the second bonding member portion. Other constituentelements for the bonding member are the same in the foldable displaydevice of the Exemplary embodiment and the foldable display device ofthe Comparative embodiment.

Referring to FIG. 9 , in the foldable display device of the Comparativeembodiment (--▪--), a flexible display panel and an optical transparentadhesive layer were separated when the number of times of bending wasapproximately 11,500, and a life-span thereof that was ended before thenumber of times of bending reaches 20,000. In contrast, the foldabledisplay device of the Exemplary embodiment (--♦--) had negligible changewhen the number of times of bending was more than 200,000.

FIG. 10 shows a plan view of an exemplary embodiment of a pixelstructure of the flexible display panel of FIG. 1 , and FIG. 11 is across-sectional view taken along line IX-IX in FIG. 10 . The flexibledisplay panel is not limited to a structure that will be hereinafterdescribed, and may include an organic light emitting diode display orliquid crystal display having a different structure.

The flexible display panel 10 may include a plurality of pixels definedtherein. Referring to FIG. 10 and FIG. 11 , the flexible display panel10 includes a pixel circuit DC and an organic light emitting diode OLEDdisposed in each pixel. The pixel circuit DC basically includes aswitching thin film transistor 50, a driving thin film transistor 60 anda capacitor 70. In addition, the flexible display panel 10 includes gatelines 81 elongated in a first direction, and arranged along a seconddirection different than the first direction. Data lines 82 and commonpower lines 83 of the flexible display panel 10 may be elongated in thesecond direction and cross the gate lines 81, while being arranged inthe first direction, but the invention is not limited thereto. The gatelines 91 are insulated from the data lines 83.

In one exemplary embodiment, one pixel may be defined by a boundary ofthe gate line 81, the data line 82 and the common power line 83, but theinvention is not limited thereto. The term pixel means a basic unit thatdisplays an image. The flexible display panel 10 displays an imagethrough the plurality of pixels.

In FIG. 10 , one pixel of an active matrix flexible display panel 10 mayinclude a two thin film transistor-one capacitor (“2Tr-1Cap”) structure.In this structure, two thin film transistors 50 and 60 and one capacitor70 are provided in the one pixel. However, the structure of the flexibledisplay panel 10 is not limited to the illustrated exemplary embodiment.The flexible display panel 10 may include three or more thin filmtransistors and two or more capacitors in a pixel. An additional wiremay be further disposed in the flexible display panel 10 so that theflexible display panel 10 may have various structures.

The organic light emitting diode OLED includes a pixel electrode 91, anorganic emission layer 92 and a common electrode 93. One of the pixelelectrode 91 and the common electrode 93 may be a hole injectionelectrode and the other may be an electron injection electrode. Light isemitted when electrons and holes are injected from the pixel electrode91 and the common electrode 93 into the organic emission layer 92, andexcitons in which the holes and the electrons are combined with eachother is reduced from an exited state to a base state.

The pixel electrode 91 may include a metal having high reflectance andthe common electrode 93 may include a transparent conductive materiallayer. Where the pixel electrode 91 includes a reflective material andthe common electrode 93 includes a transparent material, the light ofthe organic emission layer 92 is reflected by the pixel electrode 91 andtransmitted through the common electrode 93 and an encapsulationsubstrate 45, so as to be emitted to outside the flexible display panel10. In FIG. 11 , the reference numeral 40 denotes a flexible substrate.

The capacitor 70 includes a pair of capacitor electrodes 71 and 72disposed overlapping each other, and an interlayer insulating layer 85is interposed therebetween. Here, the interlayer insulating layer 85 isa dielectric material. Charges charged in the capacitor 70, and avoltage between the two capacitor electrodes 71 and 72 determinecapacitance.

The switching thin film transistor 50 includes a switching semiconductorlayer 51, a switching gate electrode 52, a switching source electrode 53and a switching drain electrode 54. The driving thin film transistor 60includes a driving semiconductor layer 61, a driving gate electrode 62,a driving source electrode 63 and a driving drain electrode 64.

The switching thin film transistor 50 is used as a switch that selects apixel for light emission. The switching gate electrode 52 is connectedto a gate line 81 among the gate lines 81. The switching sourceelectrode 53 is connected to a data line 82 among the data line 82, andthe switching drain electrode 54 is connected to one electrode 71 amongthe capacitor electrodes 71 and 72.

The driving thin film transistor 60 applies driving power to the pixelelectrode 91 for light emission of an organic emission layer 92 of theselected pixel. The driving gate electrode 62 is connected with thecapacitor electrode 71 that is connected with the switching drainelectrode 54. The driving source electrode 63 and the other capacitorelectrode 72 are connected with the common power line 83. The drivingdrain electrode 64 is connected with the pixel electrode 91 of theorganic light emitting diode OLED through a contact hole defined in alayer between the driving drain electrode 64 and the pixel electrode 91.

The switching thin film transistor 50 is driven by a gate voltageapplied to the gate line 81 and transmits a data voltage applied to thedata line 82 to the driving thin film transistor 60. A voltagecorresponds to a difference between a common voltage applied to thedriving thin film transistor 60 from the common power line 83 and thedata voltage transmitted from the switching thin film transistor 50 andis stored in the capacitor 70, and a current corresponding to thevoltage stored in the capacitor 70 flows to the organic light emittingdiode OLED through the driving thin film transistor 60 and thus theorganic emission layer 92 emits light.

The thin film encapsulation layer 45 may include a structure in which atleast one organic layer and at least one inorganic layer are alternatelylayered. The organic layer of the thin film encapsulating layer 45 mayinclude polymer, and may be a monolayer, or a multi-layer including, forexample, polyethylene terephthalate, polyimide, polycarbonate, epoxy,polyethylene, polyacrylate or a combination thereof. The inorganic layerof the thin film encapsulating layer 45 may be a monolayer or amulti-layer containing a metal oxide and/or a metal nitride. In oneexemplary embodiment, for example, the inorganic layer may includesilicon nitride (SiNx), Al2O3, SiO2, TiO2 or a combination thereof. Theuppermost layer of the thin film encapsulation layer 45, exposed to theexternal environment, may include an inorganic layer so as to preventpermeation of moisture and/or oxygen into the organic light emittingdiode OLED.

According to one or more exemplary embodiments, a bending stressgenerated when the flexible display panel is folded can be released byusing a bonding member. Thus, a stress generated in the flexible displaypanel can be released, and accordingly, damage to the flexible displaypanel can be reduced or effectively prevented and durability thereof canbe improved.

While this disclosure has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A foldable display device comprising: a hingeportion; a first support and a second support respectively coupled tothe hinge portion disposed between the first support and the secondsupport; a flexible display panel comprising: a bendable areacorresponding to the hinge portion, a first planar area and a secondplanar area respectively at opposing sides of the bendable area andrespectively corresponding to the first support and the second support;a first bonding member disposed overlapping both the first support andthe first planar area along a thickness direction of the flexibledisplay panel, and a second bonding member disposed overlapping both thesecond support and the second planar area along the thickness directionof the flexible display panel, wherein the first bonding member has afirst bonding force, wherein the second bonding member has a secondbonding force, wherein the first bonding force is different from thesecond bonding force, wherein at least one of a first distance betweenthe first planar area and the first support, and a second distancebetween the second planar area and the second support has a differentvalue before and after the flexible display panel is folded, and whereinthe first distance and the second distance are defined in a directionperpendicular to the flexible display panel.
 2. The foldable displaydevice of claim 1, wherein at least one of the first distance and thesecond distance has a different value near the bendable area before andafter the flexible display panel is folded.
 3. The foldable displaydevice of claim 2, wherein at least one of the first distance and thesecond distance is increased near the bendable area when the flexibledisplay panel is folded.
 4. The foldable display device of claim 1,wherein the flexible display panel contacts the hinge portion at thebendable area when the flexible display panel is folded.
 5. The foldabledisplay device of claim 1, wherein the flexible display panel does notcontact the hinge portion at the bendable area when the flexible displaypanel is not folded.
 6. The foldable display device of claim 1, whereinthe first bonding member comprises an adhesive having an elongationcharacteristic, and wherein the first bonding member is pulled withrespect to the first support along a plane direction of the flexibledisplay panel when the flexible display panel is folded.
 7. The foldabledisplay device of claim 1, wherein the first bonding member and thesecond bonding member respectively comprises an adhesive having anelongation characteristic, and is displaceable with respect to acorresponding support along a plane direction of the flexible displaypanel when the flexible display panel is folded.
 8. The foldable displaydevice of claim 1, wherein the first bonding member has a firstmaterial, wherein the second bonding member has a second material, andwherein the first material is different from the second material.
 9. Thefoldable display device of claim 1, further comprising a gap between thefirst bonding member and the second bonding member.
 10. The foldabledisplay device of claim 9, wherein the gap between the first bondingmember and the second bonding member is defined between the flexibledisplay panel and the hinge portion along the thickness direction of theflexible display panel, and between the first bonding member and thesecond bonding member along a plane direction of the flexible displaypanel.
 11. The foldable display device of claim 9, wherein the gapextends to each of the first planar area and the second planar areathrough each of rotation shafts of the hinge portion.
 12. The foldabledisplay device of claim 1, further comprising: a cover window disposedat external side of a display side of the flexible display panel, and atouch screen panel disposed between the flexible display panel and thecover window.